SNIP> Their reaoning is that the T&P discharge line only need to “drain dry away from the valve so the valve does not corrode closed, the pressure from the valve will blow the line clear after it releases”, the line doesn’t need to drain dry its entire length. I have been unsuccessful in changing their minds. >SNIP
I propose an experiment for the Florida inspectors. They could repeat the tests done by the relief valve manufacturers that show the explosion produced by water heaters when reliefs were not used. This time they can do the experiment with a 3/4 relief line trapped with a gallon of water in the line. You might be able to convince them to stand behind a barrier during the experiment.